1. Field of the Invention
The present invention relates to motor-driven pumps having mechanical frontal seals used to move liquids such as in household appliances, heating systems, hydraulic circulation systems in motor vehicles including industrial vehicles, and more specifically, self-unblocking motor driven pumps.
2. Description of Related Art
It is known that it is hard to start motor-driven pumps having frontal seals, especially after having been idle for a period of time. The difficulty in starting is caused by the sticking together of the frontal seals. The frontal seals have two reciprocally sliding and mirror-polished faces that ensure a hermetic seal in a certain place on a motor-driven shaft that rotates a disk wheel on the inside of a sealed chamber full of liquid to be removed. Typically, the frontal seals consist of a fixed gasket and a rotated gasket. The fixed gasket is mounted to a fixed structure of the pump. The fixed gasket has a rigid ring with a central hole through which the drive-shaft passes. The rotated gasket has an elastic element hermetically applied to the shaft and a rigid ring element surrounding the shaft.
The hermetic seal is ensured by abutting surfaces of the two rigid ring elements. These surfaces are flat, parallel, mirror-polished, and pressed together in a direction orthogonal to their common plane.
During operation the surfaces rub but their characteristics of construction and assembly ensure the desired seal. After an idle period, however, for various reasons the surfaces stick together to block rotation of the shaft. The sticking together is mainly due to the deposit of substances such as limestone, detergent, and grease, that are contained in the liquid, a drop in temperature making the substances more viscous, and the fact the two surfaces are pressing against each other. To obviate this almost systematic inconvenience, pump manufacturers must provide extra starting torque of the motor or make it possible for the user to intervene manually. The former solution is practical and feasible but calls for over sizing windings and a starting capacitor which increases manufacturing costs. The latter solution cannot practically be proposed for an entire category of uses because of inaccessibility of the pump or because automatic machines by definition do not allow manual intervention by the user to start them.
It would therefore be desirable, and is an aim of this invention, to achieve a hermetic coupling on a pump's drive-shaft that eliminates the problem described and that is reliable, economical, and easy to install using materials and techniques known in the state of the art.